Method and apparatus for video coding

ABSTRACT

An apparatus for video coding includes processing circuitry that encodes prediction information of a current block in a video bitstream. The prediction information indicates a first set of intra prediction direction mode numbers for the current block. The processing circuitry determines whether a first intra prediction direction mode number of a neighboring block of the current block is in the first set of intra prediction direction mode numbers. In response to the first intra prediction direction mode number not being in the first set of intra prediction direction mode numbers, the processing circuitry determines a most probable mode for the current block based on a second intra prediction direction mode number in the first set of intra prediction direction mode numbers that is nearest to the first intra prediction direction mode number. The processing circuitry encodes the current block based on the most probable mode of the current block.

INCORPORATION BY REFERENCE

This application is a continuation of U.S. patent application Ser. No.16/808,287, “METHOD AND APPARATUS FOR VIDEO CODING,” filed on Mar. 3,2020, which is a continuation of U.S. patent application Ser. No.16/374,535, “METHOD AND APPARATUS FOR VIDEO CODING,” filed on Apr. 3,2019 and issued as U.S. Pat. No. 10,623,748 on Apr. 14, 2020, which is acontinuation of U.S. patent application Ser. No. 16/147,246, “METHOD ANDAPPARATUS FOR VIDEO CODING,” filed on Sep. 28, 2018 and issued as U.S.Pat. No. 10,284,860 on May 7, 2019, which claims the benefit of priorityto U.S. Provisional Application No. 62/693,050, “METHODS AND APPARATUSFOR WIDE ANGULAR INTRA PREDICTION IN VIDEO COMPRESSION,” filed on Jul.2, 2018. The entire disclosures of the above-identified applications areincorporated herein by reference in their entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate), of, for example 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GByte of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reducing aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signal is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision contribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transform,quantization, and entropy coding.

Video codec technologies can include techniques known as intra coding.In Intra coding, sample values are represented without reference tosamples or other data from previously reconstructed reference pictures.In some video codecs, the picture is spatially subdivided into blocks ofsamples. When all blocks of samples are coded in intra mode, thatpicture can be an intra picture. Intra pictures and their derivationssuch as independent decoder refresh pictures, can be used to reset thedecoder state and can, therefore, be used in as the first picture in acoded video bitstream and a video session, or as a still image. Thesamples of an intra block can be exposed to a transform, and thetransform coefficients can be quantized before entropy coding. Intraprediction can be a technique that minimizes sample values in thepre-transform domain. In some cases, the smaller the DC value after atransform is, and the smaller the AC coefficients are, the fewer bitsare required at a given quantization step size to represent the blockafter entropy coding.

Traditional intra coding such as known from, for example MPEG-2generation coding technologies does not use intra prediction. However,some newer video compression technologies include techniques thatattempt, from, for example, surrounding sample data and/or metadataobtained during the encoding/decoding of spatially neighboring, andpreceding in decoding order, blocks of data. Such techniques arehenceforth called “intra prediction” techniques. Note that in at leastsome cases, intra prediction is only using reference data from thecurrent picture under reconstruction and not from reference pictures.

There can be many different forms of intra prediction. When more thanone of such techniques can be used in a given video coding technology,the technique in use can be coded in an intra prediction mode. Incertain cases, modes can have submodes and/or parameters, and those canbe coded individually or included in the mode codeword. Which codewordto use for a given mode/submode/parameter combination can have an impactin the coding efficiency gain through intra prediction, and so can theentropy coding technology used to translate the codewords into abitstream.

A certain mode of intra prediction was introduced with H.264, refined inH.265, and further refined in newer coding technologies such as jointexploration model (JEM), versatile video coding (VVC), benchmark set(BMS). A predictor block can be formed using neighboring samples valuesbelonging to already available samples. Sample values of neighboringsamples are copied into the predictor block according to a direction. Areference to the direction in use can be coded in the bitstream or mayitself be predicted.

Referring to FIG. 1, depicted in the lower right is a subset of ninepredictor directions known from H.265's 35 possible predictordirections. The point where the arrows converge (101) represents thesample being predicted. The arrows represent the direction from whichthe sample is being predicted. For example, arrow (102) indicates thatsample (101) is predicted from a sample or samples to the upper right,at a 45 degree angle from the horizontal. Similarly, arrow (103)indicates that sample (101) is predicted from a sample or samples to thelower right of sample (101), in a 22.5 degree angle from the horizontal.

Still referring to FIG. 1, on the top right there is depicted a squareblock (104) of 4×4 samples (indicated by a dashed, boldface line). Thesquare block (104) incudes 16 samples, each labelled with an “S”, itsposition in Y dimension (e.g., row index) and its position in Xdimension (e.g., column index). For example, sample S21 is the secondsample in Y dimensions (from the top) and the first (from the left)sample in X dimension. Similarly, sample S44 is the fourth sample inblock (104) in both Y and X dimension. As the block is 4×4 samples insize, S44 is at the bottom right. Further shown are reference samples,that follow a similar numbering scheme. A reference sample is labelledwith an R, its Y position (e.g., row index) and X position (columnindex) relative to block (104). In both H.264 and H.265, predictionsamples neighbor the block under reconstruction; therefore no negativevalues need to be used.

Intra picture prediction can work by copying reference sample valuesfrom the neighboring samples as appropriated by the signaled predictiondirection. For example, assume the coded video bitstream includessignaling that, for this block, indicates a prediction directionconsistent with arrow (102)—that is, samples are predicted fromprediction sample or samples to the upper right, at a 45 degree anglefrom the horizontal. In that case, samples S41, S32, S23, and S14 arepredicted from same R05. Sample S44 is then predicted from R08.

In certain cases, the values of multiple reference samples may becombined, for example through interpolation, in order to calculate areference sample; especially when the directions are not evenlydivisible by 45 degrees.

The number of possible directions has increased as video codingtechnology developed. In H.264 (year 2003), nine different directioncould be represented. That increased to 33 in H.265 (year 2013), andJEM/VVC/BMS, at the time of disclosure, can support up to 65 directions.Experiments have been conducted to identify the most likely directions,and certain techniques in the entropy coding are used to represent thoselikely directions in a small number of bits, accepting a certain penaltyfor less likely directions. Further, the directions themselves can besometimes be predicted from neighboring directions used in neighboring,already decoded, blocks.

FIG. 2 a schematic 201 that depicts 65 intra prediction directionsaccording to JEM to illustrate the increasing number of predictiondirections over time.

The mapping of an intra prediction directions bits in the coded videobitstream that represent the direction can be different form videocoding technology to video coding technology; and can range, forexample, from simple direct mappings of prediction direction to intraprediction mode to codewords, to complex adaptive schemes involving mostprobably modes and similar techniques. A person skilled in the art isreadily familiar with those techniques. In all cases, however, there canbe certain directions that are statistically less likely to occur invideo content than certain other directions. As the goal of videocompression is the reduction of redundancy, those less likely directionswill, in a well working video coding technology, be represented by alarger number of bits than more likely directions.

SUMMARY

Aspects of the disclosure provide method and apparatus for video coding.In some examples, an apparatus includes receiving circuitry andprocessing circuitry.

According to an aspect of the current disclosure, a method for videodecoding in a decoder is provided. In the disclosed method, predictioninformation of a first block from a coded video bitstream is decoded.The first block is a non-square block and the prediction information ofthe first block is indicative of a first intra prediction direction modein a first set of intra prediction direction modes that is associatedwith the non-square block. The first set of intra prediction directionmodes has a first number of different intra prediction direction modesfrom a second set of intra prediction direction modes that is associatedwith a square block. The first number is a positive integer that isbased on an aspect ratio of the first block. At least one sample of thefirst block is subsequently reconstructed according to the first intraprediction direction mode.

The disclosed method further includes decoding a syntax element from thecoded video bitstream, and the syntax element is indicative of the firstnumber. The syntax element is in at least one of a sequence parameterset, a picture parameter set, a slice header, a common syntax elementfor a region of a picture, and a common parameter for the region of thepicture.

In some embodiments, a second number of intra prediction direction modesin the second set of intra prediction direction modes are not in thefirst set of intra prediction direction modes, and the second number isa positive integer that is based on the aspect ratio of the first block.

In some embodiments, the first number is equal to the second number. Thefirst intra prediction direction mode is not in the second set of intraprediction direction modes that is associated with the square block.

In some embodiments, the first number is a fixed value that isindependent of a shape of the first block.

The disclosed method further includes calculating the aspect ratio ofthe first block and determining the first number based on the aspectratio of the first block. The second number of intra predictiondirection modes is removed in the second set of intra predictiondirection modes, and the first number of different intra predictiondirection modes is added in the second set of intra prediction directionmodes to form the first set of intra prediction direction modes.

According to another aspect of the present disclosure, an apparatus isprovided. The apparatus has processing circuitry. The processingcircuitry is configured to perform the disclosed method for videocoding.

Aspects of the disclosure also provide a non-transitorycomputer-readable medium storing instructions which when executed by acomputer for video decoding cause the computer to perform the method forvideo coding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a schematic illustration of a subset of intra prediction modesin accordance with H.265;

FIG. 2 is an illustration of intra prediction directions according toJEM;

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system (300) in accordance with an embodiment;

FIG. 4 is a schematic illustration of a simplified block diagram of acommunication system (400) in accordance with an embodiment;

FIG. 5 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment;

FIG. 6 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment;

FIG. 7 shows a block diagram of an encoder in accordance with anotherembodiment;

FIG. 8 shows a block diagram of a decoder in accordance with anotherembodiment;

FIG. 9 shows a schematic diagram that illustrates an example of wideangular modes;

FIG. 10 illustrates an example of remapping some conventional intraprediction modes to wide angle modes;

FIG. 11 illustrates another example of remapping some conventional intraprediction modes to wide angle modes;

FIG. 12 shows a schematic diagram that illustrates conventional intraprediction directions and wide angle intra prediction directions;

FIG. 13 shows a flow chart outlining a decoding process according to anembodiment of the disclosure; and

FIG. 14 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 3 illustrates a simplified block diagram of a communication system(300) according to an embodiment of the present disclosure. Thecommunication system (300) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (350). Forexample, the communication system (300) includes a first pair ofterminal devices (310) and (320) interconnected via the network (350).In the FIG. 3 example, the first pair of terminal devices (310) and(320) performs unidirectional transmission of data. For example, theterminal device (310) may code video data (e.g., a stream of videopictures that are captured by the terminal device (310)) fortransmission to the other terminal device (320) via the network (350).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (320) may receive the codedvideo data from the network (350), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (300) includes a secondpair of terminal devices (330) and (340) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (330) and (340)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (330) and (340) via the network (350). Eachterminal device of the terminal devices (330) and (340) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (330) and (340), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 3 example, the terminal devices (310), (320), (330) and(340) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (350) represents any number ofnetworks that convey coded video data among the terminal devices (310),(320), (330) and (340), including for example wireline (wired) and/orwireless communication networks. The communication network (350) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(350) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 4 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (413), that caninclude a video source (401), for example a digital camera, creating forexample a stream of video pictures (402) that are uncompressed. In anexample, the stream of video pictures (402) includes samples that aretaken by the digital camera. The stream of video pictures (402),depicted as a bold line to emphasize a high data volume when compared toencoded video data (404) (or coded video bitstreams), can be processedby an electronic device (420) that includes a video encoder (403)coupled to the video source (401). The video encoder (403) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (404) (or encoded video bitstream (404)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (402), can be stored on a streamingserver (405) for future use. One or more streaming client subsystems,such as client subsystems (406) and (408) in FIG. 4 can access thestreaming server (405) to retrieve copies (407) and (409) of the encodedvideo data (404). A client subsystem (406) can include a video decoder(410), for example, in an electronic device (430). The video decoder(410) decodes the incoming copy (407) of the encoded video data andcreates an outgoing stream of video pictures (411) that can be renderedon a display (412) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (404),(407), and (409) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Codingor VVC. The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (420) and (430) can includeother components (not shown). For example, the electronic device (420)can include a video decoder (not shown) and the electronic device (430)can include a video encoder (not shown) as well.

FIG. 5 shows a block diagram of a video decoder (510) according to anembodiment of the present disclosure. The video decoder (510) can beincluded in an electronic device (530). The electronic device (530) caninclude a receiver (531) (e.g., receiving circuitry). The video decoder(510) can be used in the place of the video decoder (410) in the FIG. 4example.

The receiver (531) may receive one or more coded video sequences to bedecoded by the video decoder (510); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (501), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (531) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (531) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (515) may be coupled inbetween the receiver (531) and an entropy decoder/parser (520) (“parser(520)” henceforth). In certain applications, the buffer memory (515) ispart of the video decoder (510). In others, it can be outside of thevideo decoder (510) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (510), forexample to combat network jitter, and in addition another buffer memory(515) inside the video decoder (510), for example to handle playouttiming. When the receiver (531) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (515) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (515) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (510).

The video decoder (510) may include the parser (520) to reconstructsymbols (521) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (510),and potentially information to control a rendering device such as arender device (512) (e.g., a display screen) that is not an integralpart of the electronic device (530) but can be coupled to the electronicdevice (530), as was shown in FIG. 5. The control information for therendering device(s) may be in the form of Supplementary EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (520) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (520) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (520) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (520) may perform entropy decoding/parsing operation on thevideo sequence received from the buffer memory (515), so as to createsymbols (521).

Reconstruction of the symbols (521) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (520). The flow of such subgroup control information between theparser (520) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (510)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (551). Thescaler/inverse transform unit (551) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (521) from the parser (520). The scaler/inversetransform unit (551) can output blocks comprising sample values, thatcan be input into aggregator (555).

In some cases, the output samples of the scaler/inverse transform (551)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (552). In some cases, the intra pictureprediction unit (552) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (558). The currentpicture buffer (558) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(555), in some cases, adds, on a per sample basis, the predictioninformation the intra prediction unit (552) has generated to the outputsample information as provided by the scaler/inverse transform unit(551).

In other cases, the output samples of the scaler/inverse transform unit(551) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (553) canaccess reference picture memory (557) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (521) pertaining to the block, these samples can beadded by the aggregator (555) to the output of the scaler/inversetransform unit (551) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (557) from where themotion compensation prediction unit (553) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (553) in the form of symbols (521) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (557) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (555) can be subject to variousloop filtering techniques in the loop filter unit (556). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (556) as symbols (521) from the parser (520), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (556) can be a sample stream that canbe output to the render device (512) as well as stored in the referencepicture memory (557) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (520)), the current picture buffer (558) can becomea part of the reference picture memory (557), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (510) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as document in thevideo compression technology or standard. Specifically, a profile canselect a certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (531) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (510) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 6 shows a block diagram of a video encoder (603) according to anembodiment of the present disclosure. The video encoder (603) isincluded in an electronic device (620). The electronic device (620)includes a transmitter (640) (e.g., transmitting circuitry). The videoencoder (603) can be used in the place of the video encoder (403) in theFIG. 4 example.

The video encoder (603) may receive video samples from a video source(601)(that is not part of the electronic device (620) in the FIG. 6example) that may capture video image(s) to be coded by the videoencoder (603). In another example, the video source (601) is a part ofthe electronic device (620).

The video source (601) may provide the source video sequence to be codedby the video encoder (603) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . )and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (601) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (601) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focusses on samples.

According to an embodiment, the video encoder (603) may code andcompress the pictures of the source video sequence into a coded videosequence (643) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (650). In some embodiments, the controller(650) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (650) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. The controller (650) can be configured to have other suitablefunctions that pertain to the video encoder (603) optimized for acertain system design.

In some embodiments, the video encoder (603) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (630) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (633)embedded in the video encoder (603). The decoder (633) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (634). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (634) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (633) can be the same as of a“remote” decoder, such as the video decoder (510), which has alreadybeen described in detail above in conjunction with FIG. 5. Brieflyreferring also to FIG. 5, however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (645) and the parser (520) can be lossless, the entropy decodingparts of the video decoder (510), including the buffer memory (515), andparser (520) may not be fully implemented in the local decoder (633).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (630) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously-coded picture fromthe video sequence that were designated as “reference pictures”. In thismanner, the coding engine (632) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (633) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (630). Operations of the coding engine (632) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 6), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (633) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (634). In this manner, the video encoder(603) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (635) may perform prediction searches for the codingengine (632). That is, for a new picture to be coded, the predictor(635) may search the reference picture memory (634) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(635) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (635), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (634).

The controller (650) may manage coding operations of the source coder(630), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (645). The entropy coder (645)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies known to a person skilled in the art as, for exampleHuffman coding, variable length coding, arithmetic coding, and so forth.

The transmitter (640) may buffer the coded video sequence(s) as createdby the entropy coder (645) to prepare for transmission via acommunication channel (660), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(640) may merge coded video data from the video coder (603) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (650) may manage operation of the video encoder (603).During coding, the controller (650) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of Intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A Predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A Bi-directionally Predictive Picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference pictures. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (603) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (603) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (640) may transmit additional datawith the encoded video. The source coder (630) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, Supplementary EnhancementInformation (SEI) messages, Visual Usability Information (VUI) parameterset fragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to Intra prediction) makes uses of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first and a second reference picture thatare both prior in decoding order to the current picture in the video(but may be in the past and future, respectively, in display order) areused. A block in the current picture can be coded by a first motionvector that points to a first reference block in the first referencepicture, and a second motion vector that points to a second referenceblock in the second reference picture. The block can be predicted by acombination of the first reference block and the second reference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels and the like.

FIG. 7 shows a diagram of a video encoder (703) according to anotherembodiment of the disclosure. The video encoder (703) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (703) is used in theplace of the video encoder (403) in the FIG. 4 example.

In an HEVC example, the video encoder (703) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (703) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (703) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(703) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (703) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 7 example, the video encoder (703) includes the interencoder (730), an intra encoder (722), a residue calculator (723), aswitch (726), a residue encoder (724), a general controller (721) and anentropy encoder (725) coupled together as shown in FIG. 7.

The inter encoder (730) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique.

The intra encoder (722) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform and, in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques).

The general controller (721) is configured to determine general controldata and control other components of the video encoder (703) based onthe general control data. In an example, the general controller (721)determines the mode of the block, and provides a control signal to theswitch (726) based on the mode. For example, when the mode is the intra,the general controller (721) controls the switch (726) to select theintra mode result for use by the residue calculator (723), and controlsthe entropy encoder (725) to select the intra prediction information andinclude the intra prediction information in the bitstream; and when themode is the inter mode, the general controller (721) controls the switch(726) to select the inter prediction result for use by the residuecalculator (723), and controls the entropy encoder (725) to select theinter prediction information and include the inter predictioninformation in the bitstream.

The residue calculator (723) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (722) or the inter encoder (730). Theresidue encoder (724) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (724) is configured to convert the residuedata in the frequency domain, and generate the transform coefficients.The transform coefficients are then subject to quantization processingto obtain quantized transform coefficients.

The entropy encoder (725) is configured to format the bitstream toinclude the encoded block. The entropy encoder (725) is configured toinclude various information according to a suitable standard, such asHEVC standard. In an example, the entropy encoder (725) is configured toinclude the general control data, the selected prediction information(e.g., intra prediction information or inter prediction information),the residue information, and other suitable information in thebitstream. Note that, according to the disclosed subject matter, whencoding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 8 shows a diagram of a video decoder (810) according to anotherembodiment of the disclosure. The video decoder (810) is configured toreceive a coded pictures that are part of a coded video sequence, anddecode the coded picture to generate a reconstructed picture. In anexample, the video decoder (810) is used in the place of the videodecoder (410) in the FIG. 4 example.

In the FIG. 8 example, the video decoder (810) includes an entropydecoder (871), an inter decoder (880), a residue decoder (873), areconstruction module (874), and an intra decoder (872) coupled togetheras shown in FIG. 8.

The entropy decoder (871) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example,intra, inter, b-predicted, the latter two in merge submode or anothersubmode), prediction information (such as, for example, intra predictioninformation or inter prediction information) that can identify certainsample or metadata that is used for prediction by the intra decoder(872) or the inter decoder (880) respectively residual information inthe form of, for example, quantized transform coefficients, and thelike. In an example, when the prediction mode is inter or bi-predictedmode, the inter prediction information is provided to the inter decoder(880); and when the prediction type is the intra prediction type, theintra prediction information is provided to the intra decoder (872). Theresidual information can be subject to inverse quantization and isprovided to the residue decoder (873).

The inter decoder (880) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (872) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (873) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (873) mayalso require certain control information (to include the QuantizerParameter QP), and that information may be provided by the entropydecoder (871) (datapath not depicted as this may be low volume controlinformation only).

The reconstruction module (874) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (873) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (403), (603) and (703), and thevideo decoders (410), (510) and (810) can be implemented using anysuitable technique. In an embodiment, the video encoders (403), (603)and (703), and the video decoders (410), (510) and (810) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (403), (603) and (603), and the videodecoders (410), (510) and (810) can be implemented using one or moreprocessors that execute software instructions.

According to some aspects of the disclosure, for intra predictions, wideangular modes can be used to compress video and reduce bandwidth orstorage space requirements.

FIG. 9 shows a schematic diagram (900) that illustrates an example ofwide angular modes. Generally, the intra prediction is within adirection at 45 degrees in top-right (corresponding to arrow pointing to34 in FIG. 9) to a direction at 45 degree in bottom-left direction(corresponding to the arrow pointing to 02 in FIG. 9), which are calledconventional intra prediction modes. The mode 2 is referred to as thebottom-left diagonal mode and the mode 34 is referred to as thetop-right diagonal mode when 35 HEVC intra prediction modes are applied.Wide angles beyond the range of prediction directions covered byconventional intra prediction modes can correspond to wide angular intraprediction modes.

In some examples, a wide-angular intra prediction direction isassociated with one conventional intra prediction direction. Forexample, a wide-angular intra prediction direction and its associatedintra prediction direction captures the same directionality, but usingreference samples of opposite sides (left column or top row). In anexample, a wide-angular intra prediction mode is signaled by sending a1-bit flag for an associated direction that has an available wide-angle“flip mode”. In the FIG. 9 example, a first direction with the arrowpointing to 35 is a wide-angular intra prediction direction, and isassociated with a second direction with the arrow pointing to 03. Thus,the first direction can be signaled by sending a 1-bit flag for thesecond direction.

In an embodiment, in the case of the 33-direction angular intraprediction, the availability of the new modes is limited to the 10directional modes closest to the 45-degree diagonal top-right mode(i.e., mode 34 when 35 conventional intra modes are applied) andbottom-left mode (i.e., mode 2 when 35 conventional intra modes areapplied). The actual sample prediction process follows the one in HEVCor VVC.

In the FIG. 9 example, 33 intra prediction directions that areassociated with mode 2 to mode 34 are shown. In an example, when a widthof a block is larger than a height of the block, directions associatedwith mode 35 and mode 36 can be used as wide-angular intra predictiondirections. Then, mode 3 and mode 4 can have extra flags indicatingwhether to use the indicated mode or flipped wide angular directionswith mode 35 and mode 36. In some examples (e.g., versatile video codingtest model 1 (VTM1)), both square and non-square blocks are supported ina quad tree, binary tree and ternary tree (QT+BT+TT) partitioningstructure. When the intra prediction design for square and non-squareblocks use the same intra prediction modes (e.g., mode 2 to mode 34) forthe square blocks, the intra prediction modes (e.g., mode 2 to mode 34in FIG. 9 example) are not efficient for non-square blocks. The wideangular prediction modes (e.g., mode 35 and mode 36 in FIG. 9 example)can be used to more efficiently encode non-square blocks.

In some examples, the signaling of wide-angle intra prediction dependson the intra prediction mode. Therefore, there is a parsing dependencyissue (intra prediction mode needs to be reconstructed during parsingprocess) when parsing the wide-angle controlling flags.

In some embodiments, some intra prediction modes for square blocks areremapped to wide angular prediction modes for non-square blocks. In anexample, during a remapping process, some intra prediction modes forsquare blocks are removed from a set of intra prediction modesoriginally used for square blocks while the same number of wide angularprediction modes is added into the set of intra prediction modes to forma new set of intra prediction modes for certain non-square blocks. Thus,a certain number of modes in the set of intra prediction modes arechanged while others are kept the same. In some examples, the certainnumber of modes that has been changed depends on a block shape, such asan aspect ratio of a block.

For square blocks, a set of conventional intra prediction modes can beused for intra prediction, and the mode number for the set ofconventional intra prediction modes can be 35, 67 and so on. Fornon-square blocks, some modes can be removed from the set ofconventional intra prediction modes and the same number of wide anglemodes (as the removed modes) can be added with the remainingconventional intra prediction modes to form a new set of intraprediction modes. As a result, in an example, the signaled mode indexfor non-square blocks and square blocks are the same, and the non-squareand square blocks share the same mode coding algorithm. In case of 35conventional intra prediction modes, the indices of added top-right wideangle modes are mode 35, mode 36, mode 37, mode 38 and so on, and theindices of added bottom-left wide angle modes are mode −1, mode −2, mode−3, mode −4 and so on.

FIG. 10 and FIG. 11 show two examples of remapping some conventionalintra prediction modes to wide angle modes. In FIG. 10, modes 2-34 areassociated with intra prediction directions as shown in FIG. 10. Themodes 2-34 are included with mode 0 and mode 1 to form a set ofconventional intra prediction modes for square blocks. In the FIG. 10example, mode 2 and mode 3 are removed (as indicated by dashed lines)from the set of conventional intra prediction modes. Further, wide anglemode 35 and mode 36 are added (as indicated by dotted lines), where thedirection of mode 35 is opposite to the direction of mode 3 (asindicated by (1001)), and the direction of mode 36 is opposite to thedirection of mode 4 (as indicated by (1002)). Thus, modes 4-36 areincluded with mode 0 and mode 1 to form a new set of intra predictionmodes for certain non-square blocks.

In FIG. 11, mode 33 and mode 34 are removed (as indicated by dashedlines), and wide angular mode −1 and mode −2 are added (as indicated bydotted lines). The direction of mode −1 is opposite to the direction ofmode 33 (as indicated by (1101)), and the direction of mode −2 is theopposite to the direction of mode 32 (as indicated by (1102)). Thus,modes −2 and −1, and modes 2-32 are included with mode 0 and mode 1 toform a new set of intra prediction modes for certain non-square blocks.

In one embodiment, the angle distance between removed conventional modesand the added wide angle modes are larger than 90 degrees and less thanor equal to 180 degrees. For example, when there are 35 conventionalintra prediction modes, and width is larger than height, mode 2 to mode5 are removed and wide angle mode 35 to mode 38 are added; when heightis larger than width, mode 31 to mode 34 are removed and mode −1 to mode−4 are added. In another example, there are 67 conventional intraprediction modes, when width is larger than height, mode 2 to mode 9 areremoved and mode 67 to mode 74 are added; when height is larger thanwidth, mode 59 to mode 66 are removed and mode −1 to mode −8 are added.

In an alternative embodiment, the removed conventional modes and theadded wide angle modes are in opposite directions. For example, whenthere are 35 conventional intra prediction modes, when width is largerthan height, mode 3 to mode 6 are removed and wide angle mode 35 to mode38 are added; when height is larger than width, mode 30 to mode 33 areremoved and wide angle mode −1 to mode −4 are added. For anotherexample, when there are 67 conventional intra prediction modes, whenwidth is larger than height, mode 3 to mode 10 are removed and wideangle mode 67 to mode 74 are added; when height is larger than width,mode 58 to mode 65 are removed and wide angle mode −1 to mode −8 areadded.

In an alternative embodiment, when width is larger than height, someconventional modes from the bottom-left direction are removed, and thesame number of wide angle modes from the top-right direction are added.Otherwise, when height is larger than width, some modes from thetop-right direction are removed, and the same number of wide angle modesfrom the bottom-left direction are added.

For example, when there are 35 conventional intra prediction modes, andwidth is larger than height, mode 2 to mode 5 are removed and wide anglemode 35 to mode 38 are added; when height is larger than width, mode 31to mode 34 are removed and wide angle mode −1 to mode −4 are added.

In an alternative embodiment, the number of removed conventional intraprediction modes is fixed for all non-square block shapes. For allnon-square blocks, N conventional intra prediction modes are removed,and N wide angle modes are added accordingly. For example, N can be 1 to7 when 35 conventional modes are used, N can be 2 to 14 when 67conventional modes are used, and N can be 4 to 28 when 129 conventionalintra prediction modes are used.

In one sub-embodiment, N can be signaled in as a high level syntaxelement, such as in sequence parameter set (SPS), picture parameter set(PPS), slice header, or as a common syntax element or parameter for aregion of a picture.

In one example, 4 conventional intra modes are removed when there are 35conventional intra prediction modes, and 8 conventional intra modes areremoved when there are 67 conventional intra prediction modes.

In an alternative embodiment, the number of removed conventional intraprediction modes depends on the shape of the non-square blocks.

In some examples, M conventional intra prediction modes are removed whenwidth/height<=2 or height/width<=2 (aspect ratio=width/height, 1<aspectratio<=2, or 1/2<=aspect ratio<1). Further, N conventional intraprediction modes are removed when width/height>=4 or height/width>=4(aspect ratio>=4 or aspect ratio<=1/4). Further, in an example, Pconventional intra prediction modes are removed when 2<aspect ratio<4 or3/4<aspect ratio<1/2. In an example, M is not equal N. In one example, Mis equal to 3 and N is equal to 5 when there are 35 conventional intraprediction modes, and M is equal to 6 and N is equal to 10 when thereare 67 conventional intra prediction modes. P can be the same as M or N,or can be different from M or N.

In one sub-embodiment, M and N can be signaled in as a high level syntaxelement, such as in sequence parameter set (SPS), picture parameter set(PPS), slice header, or as a common syntax element or parameter for aregion of a picture. In another example, the number of removedconventional intra prediction modes depends on coded information,including but not limited to block width, block height, and block widthto height ratio, block area size.

In an alternative embodiment, the removed conventional intra predictionmodes start from the bottom-left diagonal mode (i.e., mode 2 when 35modes are applied) or top-right diagonal mode (i.e., mode 34 when 35modes are applied) and the added wide angle modes start from the nearestangle beyond the bottom-left diagonal mode or the top-right diagonalmode (i.e., mode −1 or mode 35).

In some examples, the removed conventional modes and the added wideangle modes can be consecutive or non-consecutive. In one example, whenthere are 35 conventional intra prediction modes, and width is largerthan height, mode 2 to mode 5 are removed and wide angle mode 35 to mode38 are added. In another example, when there are 35 conventional intraprediction modes, and width is larger than height, mode 2 to mode 5 areremoved and wide angle mode 35, mode 37, mode 38 and mode 39 are added.

In an alternative embodiment, the unused/removed conventional intraprediction modes are used to indicate the added wide angle modes. As aresult, the unused conventional intra prediction modes are stillsignaled, but the meaning of these unused conventional intra predictionmodes are converted to the added wide angle modes. For example, whenwidth is larger than height, mode 2 is removed, but mode 2 is stillsignaled. For one non-square block, when the decoder decodes mode 2 andwidth is larger than height, the decoder will convert mode 2 to mode 35.

In an alternative embodiment, in order to derive the most probable mode(MPM) of a current block, when the intra prediction of neighboringblocks are beyond the intra prediction direction range of the currentblock, the modes of neighboring blocks will be mapped to the nearestdirection which is covered by the intra prediction direction range ofthe current block. For example, if the current block is a square block,and its left block is a non-square block and a mode number of the leftblock is 35. Mode 35 is not covered by the mode range of the currentblock. So the mode of the left block is mapped to the nearest mode 34,which is covered by the mode range of the current block.

In some embodiments, an intra prediction process is performed using wideangular prediction for a rectangular block. The intra prediction processreceives inputs, such as an intra prediction mode (denoted bypredModeIntra), a width of the current block (denoted by nWidth), aheight of the block (denoted by nHeight), neighboring samples (denotedby p[x][y] with (x=−1, y=−1 to nWidth+nHeight−1) (x=0 tonWidth+nHeight−1, y=−1), and a variable cIdx specifying the colorcomponent of the current block. The intra prediction process cangenerate predicted samples predSamples[x][y], with x=0 to nWidth−1, andy=0 to nHeight−1.

In some embodiments, the intra prediction process is performed based ona mapping between intra prediction mode predModeIntra and angleparameter intraPredAngle.

FIG. 12 shows a schematic diagram that illustrates 43 intra predictiondirections. The 43 intra prediction directions include 33 conventionalintra prediction directions that correspond to mode 2 to mode 34 of theconventional intra prediction modes, and include 5 wide angulardirections that extend beyond the mode 34 (as shown by modes 35 to 39)and 5 wide angular directions that extend beyond the mode 2 (as shown bymodes −1 to −5).

FIG. 12 also shows a top ruler (top-ruler) and a left ruler(left-ruler). In some examples, the angle parameter intraPredAngle ismeasured according to the top ruler or left ruler. Table 1 specifies amapping table between intra prediction mode predModeIntra and angleparameter intraPredAngle.

TABLE 1 predModeIntra −5 −4 −3 −2 −1 0 1 2 3 4 5 6 7 8 9 10 11intraPredAngle 114 79 60 49 39 — 32 26 21 17 13 9 5 2 0 -2 predModeIntra12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 intraPredAngle −5 −9−13 −17 −21 −26 −32 −26 −21 −17 −13 −9 −5 −2 0 2 5 predModeIntra 29 3031 32 33 34 35 36 37 38 39 intraPredAngle 9 13 17 21 26 32 39 49 60 79114

In an example, the intra prediction mode predModeIntra in the inputs isone of the conventional intra prediction modes that are removed, and theintra prediction mode predModeIntra in the inputs is converted to a wideangle mode based on an aspect ratio (nWidth/nHeight) of the currentblock.

For example, when nWidth/nHeight=2 and 2<=predModeIntra<=4,predModeIntra4←predModeIntra+33. Specifically, when the width of a blocknWidth is twice of the height of the block nHeight, 3 conventional intraprediction modes (mode 2, mode 3 and mode 4) are removed from a set ofconventional intra prediction modes, and 3 wide angle modes (mode 35,mode 36 and mode 37) are added with the remaining conventional intraprediction modes to form a new set of intra prediction modes for theblock. When the intra prediction mode predModeIntra in the inputscorresponds to one of the removed modes, the intra prediction modepredModeIntra is converted to a wide angle mode.

Further, when nWidth/nHeight>=4 and 2<=predModeIntra<=6,predModeIntra←predModeIntra+33. Specifically, when the width of a blocknWidth is equal to or more than four times of the height of the blocknHeight, 5 conventional intra prediction modes (mode 2, mode 3, mode 4,mode 5, mode 6) are removed from a set of conventional intra predictionmodes, and 5 wide angle modes (mode 35, mode 36, mode 37, mode 38 andmode 39) are added with the remaining conventional intra predictionmodes to form a new set of intra prediction modes for the block. Whenthe intra prediction mode predModeIntra in the inputs corresponds to oneof the removed modes, the intra prediction mode predModeIntra isconverted to a wide angle mode.

Further, when nHeight/nWidth=2 and 32<=predModeIntra<=34,predModeIntra←predModeIntra−35. Specifically, when the height of a blocknHeight is twice of the width of the block nWidth, 3 conventional intraprediction modes (mode 34, mode 33 and mode 32) are removed from a setof conventional intra prediction modes, and 3 wide angle modes (mode −1,mode −2 and mode −3) are added with the remaining conventional intraprediction modes to form a new set of intra prediction modes for theblock. When the intra prediction mode predModeIntra in the inputscorresponds to one of the removed modes, the intra prediction modepredModeIntra is converted to a wide angle mode.

Further, when nHeight/nWidth>=4 and 30<=predModeIntra<=34,predModeIntra←predModeIntra−35. Specifically, when the height of theblock nHeight is equal to or more than four times of the width of theblock nWidth, 5 conventional intra prediction modes (mode 34, mode 33,mode 32, mode 32, mode 30) are removed from a set of conventional intraprediction modes, and 5 wide angle modes (mode −1, mode −2, mode −3,mode −4 and mode −5) are added with the remaining conventional intraprediction modes to form a new set of intra prediction modes for theblock. When the intra prediction mode predModeIntra in the inputscorresponds to one of the removed modes, the intra prediction modepredModeIntra is converted to a wide angle mode.

Then, based on the intra prediction mode predModeIntra, thecorresponding angle parameter intraPredAngle can be determined, forexample, based on the Table 1. Then, the predicted samplespredSamples[x][y] can be calculated based on the angle parameterintraPredAngle based on a suitable video coding standard, such as anHEVC standard.

In another example, 65 conventional intra prediction directions are usedfor intra prediction of a square block. The 65 conventional intraprediction directions correspond to modes 2-66 that are conventionalintra prediction modes, such as shown in FIG. 2. The modes 2-66 and mode0 (planar mode) and mode 1 (DC mode) form a set of 67 intra predictionmodes for a square block. In some embodiments, a number of conventionalintra prediction modes are removed and a same number of wide angle modesare added to a new set of intra prediction modes for a rectangularblock, and the number depends on an aspect ratio of the rectangularblock.

In some embodiments, an intra prediction process is performed using wideangular prediction for the rectangular block (current block). The intraprediction process receives inputs, such as an intra prediction modepredModeIntra, a width of the current block nWidth, a height of theblock nHeight, neighboring samples (denoted by p[x][y] with (x=−1, y=−1to nWidth+nHeight−1) (x=0 to nWidth+nHeight−1, y=−1). The intraprediction process can generate predicted samples predSamples[x][y],with x=0 to nWidth−1, and y=0 to nHeight−1.

In an example, a variable whRatio is defined to equal to min(abs(Log2(nWidth/nHeight)), 2). When nWidth is greater than nHeight, but issmaller than two times of nHeight, whRatio is smaller than 1. WhennWidth is equal to two times of nHeight, whRatio is equal to one. WhennWidth is greater than two times of nHeight, but smaller than four timesof nHeight, whRatio is a value in the range of (1,2). When nWidth isfour times of nHeight, whRatio is equal to 2. When nWidth is more thanfour times of nHeight, whRatio is equal to 2.

Similarly, when nHeight is greater than nWidth, but is smaller than twotimes of nWidth, whRatio is smaller than 1. When nHeight is equal to twotimes of nWidth, whRatio is equal to one. When nHeight is greater thantwo times of nWidth, but smaller than four times of nWidth, whRatio is avalue in the range of (1,2). When nHeight is four times of nWidth,whRatio is equal to 2. When nHeight is more than four times of nWidth,whRatio is equal to 2. Thus, whRatio is a function of the shape of theblock, and does not depend on an orientation of the block.

In an example, the intra prediction mode predModeIntra in the inputs isone of the conventional intra prediction mode that are removed, and theintra prediction mode predModeIntra in the inputs is converted to wideangle mode based on the whRatio of the current block.

For example, when nWidth is greater than nHeight, but is smaller thantwo times of nHeight, whRatio is smaller than 1, and 6 conventionalintra prediction modes (modes 2-7) are removed from a set ofconventional intra prediction modes, and 6 wide angle modes (modes67-72) are added with the remaining conventional intra prediction modesto form a new set of intra prediction modes for the block. When theintra prediction mode predModeIntra in the inputs corresponds to one ofthe removed modes (greater than or equal to 2 and less than 8), theintra prediction mode predModeIntra is converted to a wide angle mode byadding 65.

Further, when nWidth is equal to or more than four times of nHeight, 10conventional intra prediction modes (modes 2 to 11) are removed from aset of conventional intra prediction modes, and 10 wide angle modes(modes 67 to 76) are added with the remaining conventional intraprediction modes to form a new set of intra prediction modes for theblock. When the intra prediction mode predModeIntra in the inputscorresponds to one of the removed modes (greater than or equal to 2 andless than 12), the intra prediction mode predModeIntra is converted to awide angle mode by adding 65.

Further, when nHeight is greater than nWidth, but is smaller than twotimes of nWidth, whRatio is smaller than 1, and 6 conventional intraprediction modes (modes 61-66) are removed from a set of conventionalintra prediction modes, and 6 wide angle modes (modes −1 to −6) areadded with the remaining conventional intra prediction modes to form anew set of intra prediction modes for the block. When the intraprediction mode predModeIntra in the inputs corresponds to one of theremoved modes (greater than or equal to 61 and less than 67), the intraprediction mode predModeIntra is converted to a wide angle mode bysubtracting 67.

Further, when nHeight is equal to or more than four times of nWidth, 10conventional intra prediction modes (modes 57-66) are removed from a setof conventional intra prediction modes, and 10 wide angle modes (modes−1 to −10) are added with the remaining conventional intra predictionmodes to form a new set of intra prediction modes for the block. Whenthe intra prediction mode predModeIntra in the inputs corresponds to oneof the removed modes (greater than or equal to 57 and less than 67), theintra prediction mode predModeIntra is converted to a wide angle mode bysubtracting 67.

Then, based on the intra prediction mode predModeIntra, thecorresponding angle parameter intraPredAngle can be determined, forexample, based on a look-up table. Then, the predicted samplespredSamples[x][y] can be calculated based on the angle parameterintraPredAngle based on a suitable video coding standard, such as anHEVC standard.

FIG. 13 shows a flow chart outlining a process (1300) according to anembodiment of the disclosure. The process (1300) can be used in thereconstruction of a block coded in intra mode, so as to generate aprediction block for the block under reconstruction. In variousembodiments, the process (1300) is executed by processing circuitry,such as the processing circuitry in the terminal devices (310), (320),(330) and (340), the processing circuitry that performs functions of thevideo encoder (403), the processing circuitry that performs functions ofthe video decoder (410), the processing circuitry that performsfunctions of the video decoder (510), the processing circuitry thatperforms functions of the intra prediction module (552), the processingcircuitry that performs functions of the video encoder (603), theprocessing circuitry that performs functions of the predictor (635), theprocessing circuitry that performs functions of the intra encoder (722),the processing circuitry that performs functions of the intra decoder(872), and the like. In some embodiments, the process (1300) isimplemented in software instructions, thus when the processing circuitryexecutes the software instructions, the processing circuitry performsthe process (1300). The process starts at (S1301) and proceeds to(S1310).

At (S1310), prediction information for a block is decoded. In anexample, the processing circuitry decodes the prediction information ofthe block from a coded video bitstream. In some examples, the block is anon-square block and the prediction information of the block isindicative of a first intra prediction direction mode in a first set ofintra prediction direction modes for the non-square block. The first setof intra prediction direction modes has a first number of differentintra prediction direction modes (e.g., one or more wide angle modes)that are not in a second set of intra prediction direction modes for asquare block. The first set of intra prediction direction modes does notinclude a second number of missing (removed or unused) intra predictiondirection modes that are in the second set of intra prediction directionmodes. The first number of different intra prediction direction modesand the second number of missing intra prediction direction modes are afunction of an aspect ratio (which is indicative of the shape of theblock) of the block in some embodiments. Both the first number and thesecond number are positive integers. In some embodiments, the firstnumber is equal to the second number.

At (S1320), samples of the block are reconstructed according to thefirst intra prediction direction mode. In some examples, based on thefirst intra prediction direction mode, the corresponding angle parametercan be determined, for example, based on a look-up table. Then, thesamples of the block can be calculated based on the angle parameterbased on a suitable video coding standard, such as an HEVC standard.Then, the process proceeds to S1399 and terminates.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 14 shows a computersystem (1400) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 14 for computer system (1400) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1400).

Computer system (1400) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1401), mouse (1402), trackpad (1403), touchscreen (1410), data-glove (not shown), joystick (1405), microphone(1406), scanner (1407), camera (1408).

Computer system (1400) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1410), data-glove (not shown), or joystick (1405), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1409), headphones(not depicted)), visual output devices (such as screens (1410) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (1400) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1420) with CD/DVD or the like media (1421), thumb-drive (1422),removable hard drive or solid state drive (1423), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1400) can also include an interface to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters that attached to certain general purpose dataports or peripheral buses (1449) (such as, for example USB ports of thecomputer system (1400)); others are commonly integrated into the core ofthe computer system (1400) by attachment to a system bus as describedbelow (for example Ethernet interface into a PC computer system orcellular network interface into a smartphone computer system). Using anyof these networks, computer system (1400) can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bi-directional, for example to othercomputer systems using local or wide area digital networks. Certainprotocols and protocol stacks can be used on each of those networks andnetwork interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1440) of thecomputer system (1400).

The core (1440) can include one or more Central Processing Units (CPU)(1441), Graphics Processing Units (GPU) (1442), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1443), hardware accelerators for certain tasks (1444), and so forth.These devices, along with Read-only memory (ROM) (1445), Random-accessmemory (1446), internal mass storage such as internal non-useraccessible hard drives, SSDs, and the like (1447), may be connectedthrough a system bus (1448). In some computer systems, the system bus(1448) can be accessible in the form of one or more physical plugs toenable extensions by additional CPUs, GPU, and the like. The peripheraldevices can be attached either directly to the core's system bus (1448),or through a peripheral bus (1449). Architectures for a peripheral businclude PCI, USB, and the like.

CPUs (1441), GPUs (1442), FPGAs (1443), and accelerators (1444) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1445) or RAM (1446). Transitional data can be also be stored in RAM(1446), whereas permanent data can be stored for example, in theinternal mass storage (1447). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1441), GPU (1442), massstorage (1447), ROM (1445), RAM (1446), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1400), and specifically the core (1440) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1440) that are of non-transitorynature, such as core-internal mass storage (1447) or ROM (1445). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1440). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1440) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1446) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1444)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

APPENDIX A: ACRONYMS

-   JEM: joint exploration model-   VVC: versatile video coding-   BMS: benchmark set-   HEVC: High Efficiency Video Coding-   SEI: Supplementary Enhancement Information-   VUI: Video Usability Information-   GOPs: Groups of Pictures-   TUs: Transform Units,-   PUs: Prediction Units-   CTUs: Coding Tree Units-   CTBs: Coding Tree Blocks-   PBs: Prediction Blocks-   HRD: Hypothetical Reference Decoder-   SNR: Signal Noise Ratio-   CPUs: Central Processing Units-   GPUs: Graphics Processing Units-   CRT: Cathode Ray Tube-   LCD: Liquid-Crystal Display-   OLED: Organic Light-Emitting Diode-   CD: Compact Disc-   DVD: Digital Video Disc-   ROM: Read-Only Memory-   RAM: Random Access Memory-   ASIC: Application-Specific Integrated Circuit-   PLD: Programmable Logic Device-   LAN: Local Area Network-   GSM: Global System for Mobile communications-   LTE: Long-Term Evolution-   CANBus: Controller Area Network Bus-   USB: Universal Serial Bus-   PCI: Peripheral Component Interconnect-   FPGA: Field Programmable Gate Areas-   SSD: solid-state drive-   IC: Integrated Circuit-   CU: Coding Unit

What is claimed is:
 1. A method for video encoding in an encoder,comprising: encoding prediction information of a current block in avideo bitstream, the prediction information indicating a first set ofintra prediction direction mode numbers for the current block;determining whether a first intra prediction direction mode number of aneighboring block of the current block is in the first set of intraprediction direction mode numbers of the current block; and in responseto the first intra prediction direction mode number of the neighboringblock not being in the first set of intra prediction direction modenumbers of the current block, determining a most probable mode for thecurrent block based on a second intra prediction direction mode numberin the first set of intra prediction direction mode numbers of thecurrent block that is nearest to the first intra prediction directionmode number of the neighboring block, and encoding the current blockbased on the most probable mode of the current block.
 2. The method ofclaim 1, wherein the current block is a square block and the neighboringblock of the current block is a non-square block.
 3. The method of claim2, wherein a second set of intra prediction direction mode numbers ofthe non-square block includes a subset of the first set of intraprediction direction mode numbers of the square block and at least oneadditional intra prediction direction mode number that is different fromthe first set of intra prediction direction mode numbers of the squareblock.
 4. The method of claim 3, wherein the first intra predictiondirection mode number of the non-square block corresponds to a firstintra prediction direction that is opposite to a second intra predictiondirection, wherein an intra prediction direction mode numbercorresponding to the second intra prediction direction is in the firstset of intra prediction direction mode numbers of the square block andnot in the second set of intra prediction direction mode numbers of thenon-square block.
 5. The method of claim 3, wherein a number of the atleast one additional intra prediction direction mode number is a fixednumber that is independent of a shape of the non-square block, thenumber being from 1 to 7 when the first set of intra predictiondirection mode numbers has 33 intra prediction direction mode numbers,the number being from 2 to 14 when the first set of intra predictiondirection mode numbers has 65 intra prediction direction mode numbers,and the number being from 4 to 28 when the first set of intra predictiondirection mode numbers has 127 intra prediction direction mode numbers.6. The method of claim 3, wherein a number of the at least oneadditional intra prediction direction mode number is determined based onat least one of a width of the non-square block, a height of thenon-square block, a ratio of the width and the height of the non-squareblock, or an area of the non-square block.
 7. The method of claim 3,further comprising: encoding a syntax element in the video bitstream,the syntax element indicating a number of the at least one additionalintra prediction direction mode number, the syntax element being in atleast one of a sequence parameter set, a picture parameter set, a sliceheader, a common syntax element for a region of a picture, or a commonparameter for the region of the picture.
 8. The method of claim 3,wherein a number of the at least one additional intra predictiondirection mode number is equal to a number M when an aspect ratio of thenon-square block is equal to or less than
 2. 9. The method of claim 8,wherein the number M is equal to 3 when the first set of intraprediction direction mode numbers has 33 intra prediction direction modenumbers, and the number M is equal to 6 when the first set of intraprediction direction mode numbers has 65 intra prediction direction modenumbers.
 10. The method of claim 3, wherein a number of the at least oneadditional intra prediction direction mode number is equal to a number Nwhen an aspect ratio of the non-square block is equal to or more than 4.11. The method of claim 10, wherein the number N is equal to 5 when thefirst set of intra prediction direction mode numbers has 33 intraprediction direction mode numbers, and the number N is equal to 10 whenthe first set of intra prediction direction mode numbers has 65 intraprediction direction mode numbers.
 12. An apparatus, comprising:processing circuitry configured to: encode prediction information of acurrent block in a video bitstream, the prediction informationindicating a first set of intra prediction direction mode numbers forthe current block; determine whether a first intra prediction directionmode number of a neighboring block of the current block is in the firstset of intra prediction direction mode numbers of the current block; andin response to the first intra prediction direction mode number of theneighboring block not being in the first set of intra predictiondirection mode numbers of the current block, determine a most probablemode for the current block based on a second intra prediction directionmode number in the first set of intra prediction direction mode numbersof the current block that is nearest to the first intra predictiondirection mode number of the neighboring block, and encode the currentblock based on the most probable mode of the current block.
 13. Theapparatus of claim 12, wherein the current block is a square block andthe neighboring block of the current block is a non-square block. 14.The apparatus of claim 13, wherein a second set of intra predictiondirection mode numbers of the non-square block includes a subset of thefirst set of intra prediction direction mode numbers of the square blockand at least one additional intra prediction direction mode number thatis different from the first set of intra prediction direction modenumbers of the square block.
 15. The apparatus of claim 14, wherein thefirst intra prediction direction mode number of the non-square blockcorresponds to a first intra prediction direction that is opposite to asecond intra prediction direction, wherein an intra prediction directionmode number corresponding to the second intra prediction direction is inthe first set of intra prediction direction mode numbers of the squareblock and not in the second set of intra prediction direction modenumbers of the non-square block.
 16. The apparatus of claim 14, whereina number of the at least one additional intra prediction direction modenumber is a fixed number that is independent of a shape of thenon-square block, the number being from 1 to 7 when the first set ofintra prediction direction mode numbers has 33 intra predictiondirection mode numbers, the number being from 2 to 14 when the first setof intra prediction direction mode numbers has 65 intra predictiondirection mode numbers, and the number being from 4 to 28 when the firstset of intra prediction direction mode numbers has 127 intra predictiondirection mode numbers.
 17. The apparatus of claim 14, wherein a numberof the at least one additional intra prediction direction mode number isdetermined based on at least one of a width of the non-square block, aheight of the non-square block, a ratio of the width and the height ofthe non-square block, or an area of the non-square block.
 18. Theapparatus of claim 14, wherein the processing circuitry is furtherconfigured to: encode a syntax element in the video bitstream, thesyntax element indicating a number of the at least one additional intraprediction direction mode number, the syntax element being in at leastone of a sequence parameter set, a picture parameter set, a sliceheader, a common syntax element for a region of a picture, or a commonparameter for the region of the picture.
 19. The apparatus of claim 14,wherein a number of the at least one additional intra predictiondirection mode number is equal to a number M when an aspect ratio of thenon-square block is equal to or less than 2 and is equal to a number Nwhen an aspect ratio of the non-square block is equal to or more than 4,the number M being equal to 3 and the number N being equal to 5 when thefirst set of intra prediction direction mode numbers has 33 intraprediction direction mode numbers, and the number M being equal to 6 andthe number N being equal to 10 when the first set of intra predictiondirection mode numbers has 65 intra prediction direction mode numbers.20. A non-transitory computer-readable medium storing instructions whichwhen executed by a computer for video decoding cause the computer toperform: encoding prediction information of a current block in a videobitstream, the prediction information indicating a first set of intraprediction direction mode numbers for the current block; determiningwhether a first intra prediction direction mode number of a neighboringblock of the current block is in the first set of intra predictiondirection mode numbers of the current block; and in response to thefirst intra prediction direction mode number of the neighboring blocknot being in the first set of intra prediction direction mode numbers ofthe current block, determining a most probable mode for the currentblock based on a second intra prediction direction mode number in thefirst set of intra prediction direction mode numbers of the currentblock that is nearest to the first intra prediction direction modenumber of the neighboring block, and encoding the current block based onthe most probable mode of the current block.